A binary star is actually a pair of stars that are held together by the force of gravity. Although occasionally the individual stars that compose a binary star can be distinguished, they generally appear as one star. The gravitational pull between the individual stars 5 of a binary star causes one to orbit around the other. From the orbital pattern of a binary, the mass of its stars can be determined: the gravitational pull of a star is in direct proportion to its mass, and the strength of the gravitational force of one star on another determines the orbital pattern of the binary. Scientists 10 have discovered stars that seem to orbit around an empty space. It has been suggested that such a star and the empty space really compose a binary star. The empty space is known as a black hole, a star with such a strong gravitational force that no light is able to get through.

1. A binary star could best be described as (A) stars that have been forced apart(B) a star with a strong gravitational force(C) two stars pulled together by gravity(D) a large number of attached stars2. According to the passage, what happens as a result of the gravitational force between the stars?(A) One star circles the other.(B) The mass of the binary star increases.(C) A black hole is destroyed.(D) The gravitational force decreases.3. According to the passage, what can scientists learn from the pattern of a binary star's orbit?(A) The proportion of the star's gravitational pull to its mass(B) How to distinguish the stars that compose a binary(C) Why there is no light in a black hole(D) The mass of the stars that compose the binary4. According to the passage, what is a black hole?(A) An empty space around which nothing orbits(B) A star with close to zero gravity(C) A star whose gravitational force blocks the passage of light(D) An empty space so far away that no light can reach it5. According to the passage, what is a black hole?(A) An empty space around which nothing orbits(B) A star with close to zero gravity(C) A star whose gravitational force blocks the passage of light(D) An empty space so far away that no light can reach it6. This passage would most likely be assigned reading in a course on(A) botany(B) astrophysics(C) geology(D) astrology